The present invention is directed to an arrangement for DPCM signal coding of video signals.
An arrangement of this species that, for example is known from Proc. IEEE, Vol. 73, No. 4, Apr. 1985, pages 592 through 598, particularly FIGS. 1, 2 and 4 therein, is set forth with reference to a fundamental circuit diagram shown in FIG. 1. A sequence of digitized picture element signals s is received at an input 1 of the arrangement, these signals s being supplied via sample and hold stages that are not shown in detail. In order to reduce the data flow, an effort is made to remove redundant and irrelevant parts of the picture signal in order, for example, to be able to reduce the bit transmission rate without thereby deteriorating the picture quality. In detail, this occurs in that it is not the successive picture element signals that are transmitted via the transmission channel leading to a reception location, but rather, only the difference signals that are formed by taking the difference between a respectively current picture element signal s and an estimated value s calculated in a predictor on the basis of the preceding picture element signals are transmitted. Such a method is also referred to as difference pulse code modulation (DPCM).
German Patent Application No. P 37 14 130.9 "Anordnung zur DPCM-Codierung von Fernsehsignalen" discloses a DPCM coder wherein respective estimated values are subtracted from the digitized picture element signals and the estimated errors are used for signal transmission after quantization and coding. Every estimated value is derived from a reconstructed picture element signal formed in an adder. Separate, simultaneously subtractions of the signal taken at the adder output for both the positive and for the negative adder limit value thereby occur for the respective picture element signal of the input side. An overflow recognition means and a multiplexer provide that only that difference from the three differences formed up to this point, which is the actual addition result (not overflow, positive overflow, negative overflow) is through-connected to the quantizer. A limiter between two adders that reduces the calculating speed can thereby be eliminated in that the limiter function is distributed over three paths calculating in parallel for the positive and negative adder limit value, as well as, for the unlimited value. Three subtractors are required for the three paths in this arrangement that calculate in parallel, this denoting increased circuit complexity.
The difference formation required for a DPCM coding occurs in a subtractor 2 whose first input is connected to the input 1 and whose second input is connected to a predictor 3. Every difference signal .DELTA. that is also referred to as an estimated error is quantized in a quantizer 4, whereby the resulting difference signal, .DELTA.q=.DELTA.+q, influenced by the quantization error q is coded in a coder 5 and is supplied to a transmission channel via an output 6. A recursive signal path is provided for the formation of the estimated value s, this signal path connected from a circuit point 7 at the output side of the quantizer 4 to a second input of the subtractor 2. The path contains a first adder 8, a limiter means 9 and the predictor 3. The output of the predictor 3 is also connected to a second input of the first adder 8 that forms what is referred to as a reconstructed picture element signal S.sub.R by addition of the quantized difference signal .DELTA..sub.q and of the estimated value s. The predictor 3 supplies the estimated value s from at least one of the preceding picture element signals for every current picture element signal s.
When, according to FIG. 2, the current picture element lying in the line n in a video picture m is referenced X, the picture element sampled immediately therebefore is referenced A, the picture element of the preceding line n-1 corresponding to X is referenced C and the picture elements neighboring the latter and sampled immediately before or after that are referenced B and D and when, further, the corresponding picture elements of the preceding image m-1 are referenced X' and A' through D', the following then results: the picture element signals of at least one of the points A through D can be utilized for the formation of the estimated value s for the picture element signal of X, whereby one speaks of a two-dimensional (2D) prediction. When the picture element signals of at least one of the picture elements X' and A' through D' are employed exclusively or in addition thereto, then there is a three-dimensional (3D) prediction. In the former instance, the estimated value s can be calculated, for example, according to the 2D estimation equation: EQU s=.alpha..multidot.s.sub.A +.beta..multidot.s.sub.B +.gamma..multidot.s.sub.C +.delta..multidot.s.sub.D ( 1).
In the latter instance, for example, the estimated value s can be calculated according to the 3D estimation equation: EQU s=.alpha..multidot.s.sub.A +.beta..multidot.s.sub.X ' (2).
whereby s.sub.A references the reconstructed picture element signal of the picture element A, s.sub.B references that of the picture element B etc., and whereby the coefficients .alpha., .beta., .gamma., and .delta. represent weighing factors that are allocated to the individual picture element signals.